I06 LOWER PENINSULA. 



CYATHOPHYLLUM RUGOSUM, Milne-Edwards. 

 Synon., AsTR/EA rugosa, Hall. 



AstiTEiform colonies of polygonal, intimately united stems of 

 a diameter from one to one and a half centimeter, which in some 

 specimens of a certain state of preservation are separable, and 

 present longitudinally ribbed polygonal stems, annulated by trans- 

 verse wrinkles of growth. Calyces joining, with gradually ascend- 

 ing side walls, inclosing conical cell pits ; or the end cells are formed 

 by an abrupt, narrow, central pit, with horizontally expanded, dis- 

 coid margins. The bottom of the cells is sometimes formed by dia- 

 phragms with a smooth central spot ; usually the lamellae reach to 

 the centre and intermingle there, forming a twisted knot. Number 

 of lamellae in the circumference of the calyces from 35 to 45 ; their 

 edges are crenulated, the side faces traversed by arched carinae, which 

 in some specimens are almost obsolete, in others veiy distinct. In- 

 terlamellar interstices traversed by small vesicles filling them to 

 the margins of the calyces. The centre of the stems is transversely 

 septate by diaphragms, intersected in their outer circumference by 

 continuous vertical lamellae ; centrally their continuity is inter- 

 rupted, and the ends are merely carinations on the upper face of the 

 diaphragms. 



Milne-Edwards describes paliform lobes and the development of a 

 rudimentary columella in this species, but neither one nor the other 

 structure can be recognized. The centre of the calyces in some 

 weathered specimens protrudes with a degree of convexity exhibit- 

 ing the twisted ends of the radial lamellae, but no paliform lobes, 

 much less a columella. Found in the Helderberg limestones of 

 Mackinac Island, and in the drift of the Lower Peninsula. It is 

 also common at the Falls of the Ohio, at Sandusky, and in many 

 other localities. 



Plate XXXVII.^ — The upper row represents a polished, horizontal 

 section, and a lateral view of another specimen with stems separable 

 from each other. 



